The present invention relates to a bar code reader of the type including at least one oscillating mirror for directing scanning light toward a code. In particular, the present invention relates to a suspension which supports the mirror for oscillation about a predetermined axis.
An important consideration in designing bar code readers is the design of the structure which supports the mirror(s) of such readers for oscillation. More specifically, mirrors in stationary industrial bar code readers typically oscillate at frequencies in the range of 300-900 Hz. One goal in designing such structures is reducing the energy required to oscillate mirrors at these frequencies. Accordingly, the design of bearing and spring structures which support reader mirrors is directed to reducing the force required to oscillate the mirrors at desired frequencies. However, oscillating mirror supports need to withstand between 15-45 billion cycles to have a life in the range of five (5) years when operating at 300-900 Hz.
The combination of bearings and spring structures to support a reader mirror for oscillation provides two functions. In particular, the bearings restrict oscillation of the mirror to oscillation about a single axis, and the spring structure produces the spring force needed for oscillation. One problem with this configuration is bearings can cause dampening and consume substantial energy relative to the energy required for oscillation. As a result, various bearing and lubrication combinations have been used in an attempt to reduce dampening and energy consumption. However, oscillating bearings through less than 360 degrees of rotation causes rapid lubricate failure resulting in increased dampening and energy loss.
Fatigue failure and rotational stiffness about desired rotational axes are problems encountered with spring biased structures which support reader mirrors for oscillation. These problems have been addressed with various spring structures typically having other drawbacks such as reduce oscillatory motion and skewed oscillatory axes.
In view of the problems associated with the use of bearings, and typical spring designs, it would be desirable to provide a structure for supporting a reader mirror which does not include bearings, and includes an improved spring configuration which reduces the energy required to oscillate the associated reader mirror. Additionally, it would be desirable to provide a structure which permits a wider range of oscillating angles for the reader mirror.